[T]he human person has a right to religious freedom. This freedom means that all men are to be immune from coercion on the part of individuals or of social groups and of any human power, in such wise that no one is to be forced to act in a manner contrary to his own beliefs, whether privately or publicly, whether alone or in association with others, within due limits.
The council further declares that the right to religious freedom has its foundation in the very dignity of the human person as this dignity is known through the revealed word of God and by reason itself. This right of the human person to religious freedom is to be recognized in the constitutional law whereby society is governed and thus it is to become a civil right.
It is in accordance with their dignity as persons-that is, beings endowed with reason and free will and therefore privileged to bear personal responsibility-that all men should be at once impelled by nature and also bound by a moral obligation to seek the truth, especially religious truth. They are also bound to adhere to the truth, once it is known, and to order their whole lives in accord with the demands of truth.
…the highest norm of human life is the divine law-eternal, objective and universal-whereby God orders, directs and governs the entire universe and all the ways of the human community by a plan conceived in wisdom and love. Man has been made by God to participate in this law, with the result that, under the gentle disposition of divine Providence, he can come to perceive ever more fully the truth that is unchanging. Wherefore every man has the duty, and therefore the right, to seek the truth in matters religious in order that he may with prudence form for himself right and true judgments of conscience, under use of all suitable means.
Truth, however, is to be sought after in a manner proper to the dignity of the human person and his social nature. The inquiry is to be free, carried on with the aid of teaching or instruction, communication and dialogue, in the course of which men explain to one another the truth they have discovered, or think they have discovered, in order thus to assist one another in the quest for truth.
Moreover, as the truth is discovered, it is by a personal assent that men are to adhere to it.
On his part, man perceives and acknowledges the imperatives of the divine law through the mediation of conscience. In all his activity a man is bound to follow his conscience in order that he may come to God, the end and purpose of life. It follows that he is not to be forced to act in a manner contrary to his conscience. Nor, on the other hand, is he to be restrained from acting in accordance with his conscience, especially in matters religious. The reason is that the exercise of religion, of its very nature, consists before all else in those internal, voluntary and free acts whereby man sets the course of his life directly toward God. No merely human power can either command or prohibit acts of this kind. The social nature of man, however, itself requires that he should give external expression to his internal acts of religion: that he should share with others in matters religious; that he should profess his religion in community. Injury therefore is done to the human person and to the very order established by God for human life, if the free exercise of religion is denied in society, provided just public order is observed.
Paul VI, The Declaration of Religious Freedom, par 2 & 3.
(Vatican Council II)